源码分析篇-Android绘制流程（三）requestLayout（）与
invalidat。。。
本⽂主要探讨能够触发performTraversals()执⾏的invalidate()、postInvalidate()和requestLayout()⽅法的流程。在调⽤这三个⽅法到最后执⾏到performTraversals()⽅法，涉及到到通过Choroegrapher请求Vsync信号，实现按帧绘制的流程，所以还会介绍Choroegrapher类的⼯作流程。
⼀、requestLayout()流程
invalidate()和postInvalidate()能够触发View的重画，这两个⽅法最终会调⽤到performTraversals()中的performDraw()来完成重绘制，但是是否会执⾏onMeasure()和onLayout()过程要根据标志位的状况来决定；requesetLayout()⽅法也会调⽤到performTraversals()⽅法，但是只会执⾏measure和layout流程，不会调⽤到draw流程来触发重画动作。直接来看questLayout()代码。
@CallSuper
public void requestLayout() {
if (mMeasureCache != null) mMeasureCache.clear();
//如果当前的整个View树在进⾏布局流程的话，则会调⽤requestLayoutDuringLayout()
//让这次的布局延时执⾏
if (mAttachInfo != null && mAttachInfo.mViewRequestingLayout == null) {
// Only trigger request-during-layout logic if this is the view requesting it,
// not the views in its parent hierarchy
ViewRootImpl viewRoot = getViewRootImpl();
if (viewRoot != null && viewRoot.isInLayout()) {
if (!questLayoutDuringLayout(this)) {
return;
}
}
mAttachInfo.mViewRequestingLayout = this;
}
//PFLAG_FORCE_LAYOUT会在执⾏View的measure()和layout()⽅法时判断
//只有设置过该标志位，才会执⾏measure()和layout()流程
mPrivateFlags |= PFLAG_FORCE_LAYOUT;
mPrivateFlags |= PFLAG_INVALIDATED;
if (mParent != null && !mParent.isLayoutRequested()) {
}
if (mAttachInfo != null && mAttachInfo.mViewRequestingLayout == this) {
mAttachInfo.mViewRequestingLayout = null;
}
}
该⽅法主要是设置了PFLAG_FORCE_LAYOUT和PFLAG_INVALIDATED到当前View的Flag中，然后调⽤到当前View（当前View可能是⼀个控件View，也可能是⼀个布局View，因为对于这两类View都能调⽤requestLayout()⽅法）的⽗布局View的requestLayout()⽅法，⽗布局View是ViewGroup类型，没有重写该requestLayout()⽅法，所以实际还是调回到questLayout()⽅法的这套逻辑。这个过程，就是设置当前View标志位后，就不断的向上调⽤⽗布局View的requestLayout()，最后调⽤到根View即DecorView的requestLayout()，⽽DecorView的mParent变量指向的是当前窗⼝对应的ViewRootImpl对象，最后⼀次设置完DecorView标志位后，调⽤到questLayout()⽅法，进⼊该代码。
@Override
public void requestLayout() {
//该boolean变量会在ViewRootImpl.performLayout()开始时置为ture，结束置false
//表⽰当前不处于Layout过程
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
如果当前不是正在执⾏layout过程，则会调⽤scheduleTraversals()⽅法，进⼊ViewRootImpl.scheduleTraversals()。
void scheduleTraversals() {
if (!mTraversalScheduled) {
//在下⼀段代码处会置回false
//表⽰在排好这次绘制请求前，不再排其它的绘制请求
mTraversalScheduled = true;
mTraversalBarrier = Looper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
这⾥主要是调⽤到了ViewRootImpl的另⼀个重要的变量mChoreographer，它是Choreographer类型的，
这个对象会请求Vsync信号来控制绘制的进⾏，实现了按帧进⾏绘制的机制，这个类会在后⽂进⾏介绍。该⽅法对于绘制的请求经过了Choreographer的编排后，最终会调⽤回ViewRootImpl.doTraversal()⽅法。
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
... //⽤于调试相关代码
performTraversals();
... //⽤于调试相关代码
}
}
然后调⽤到ViewRootImpl.performTraversals()⽅法。
⼆、invalidate()与postInvalidate()流程
invalidate()与postInvalidate()都是⽤于被调⽤来触发View的更新（重画）动作，区别在于invalidate()⽅法是在UI线程⾃⾝中使⽤，⽽postInvalidate()是⾮UI线程中使⽤。⾸先来看View.postInvalidate()。
public void postInvalidate() {
postInvalidateDelayed(0);
}
public void postInvalidateDelayed(long delayMilliseconds) {
// We try only with the AttachInfo because there's no point in invalidating
// if we are not attached to our window
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
attachInfo.mViewRootImpl.dispatchInvalidateDelayed(this, delayMilliseconds);
}
}
调⽤到了对应的ViewRootImpl对象的dispatchInvalidateDelayed()⽅法，进⼊该代码。
public void dispatchInvalidateDelayed(View view, long delayMilliseconds) {
Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view);
mHandler.sendMessageDelayed(msg, delayMilliseconds);
}
这⾥实现了⼀个消息机制，发送了MSG_INVSLIDSTE。进⼊处理消息的ViewRootImpl.handleMessage()⽅法。
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_INVALIDATE:
((View) msg.obj).invalidate();
break;
...
}
这⾥实际上就是调回了调⽤postInvalidate()⽅法的View的invalidate()⽅法。由于invalidate()⽅法只能在UI线程执⾏，所以postInvalidate 只是实现了⼀个消息机制，让⽤户能够在⾮UI线程使⽤，最终还是调⽤到invalidate()⽅法来触发重画，实现界⾯更新动作。继续来看View.invalidate()⽅法，该⽅法逻辑的实际实际上时调⽤到invalidateInternal()⽅法来实现的。
public void invalidate() {
invalidate(true);
}
void invalidate(boolean invalidateCache) {
//mLeft、mRigth、mTop、mBottom记录的是当前View边界距离其⽗布局View边界的距离
invalidsinvalidateInternal(0, 0, mRight - mLeft, mBottom - mTop, invalidateCache, true);
}
void invalidateInternal(int l, int t, int r, int b, boolean invalidateCache,
boolean fullInvalidate) {
if (mGhostView != null) {
mGhostView.invalidate(true);
return;
}
//如果当前视图为不可见状态且没有动画正在执⾏，且其⽗布局也没有过渡动画执⾏，则跳过
if (skipInvalidate()) {
return;
}
//当前View没有正在执⾏该⽅法
//或绘制缓存可⽤或未重绘过或透明度发⽣改变
//PFLAG_DRAWN会在该⽅法内去改标志位
//PFLAG_INVALIDATED会在View.draw()⽅法执⾏时去掉该标志位
if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)) == (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)
|| (invalidateCache && (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID)
|| (mPrivateFlags & PFLAG_INVALIDATED) != PFLAG_INVALIDATED
|| (fullInvalidate && isOpaque() != mLastIsOpaque)) {
//如果需要全部重绘，invalidate()未传参调⽤时默认为true
if (fullInvalidate) {
mLastIsOpaque = isOpaque();
mPrivateFlags &= ~PFLAG_DRAWN;
}
mPrivateFlags |= PFLAG_DIRTY;
if (invalidateCache) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
// Propagate the damage rectangle to the parent view.
//damage记录的区域是需要更新的dirty区域，当前的坐标时相对于⾃⾝来设置的
//通过不断调⽤到⽗类的invalidateChild()⽅法，来不断更新dirty区域的相对坐标
final AttachInfo ai = mAttachInfo;
final ViewParent p = mParent;
if (p != null && ai != null && l < r && t < b) {
final Rect damage = ai.mTmpInvalRect;
damage.set(l, t, r, b);
p.invalidateChild(this, damage);
}
/
/ Damage the entire projection receiver, if necessary.
if (mBackground != null && mBackground.isProjected()) {
final View receiver = getProjectionReceiver();
if (receiver != null) {
receiver.damageInParent();
}
}
// Damage the entire IsolatedZVolume receiving this view's shadow.
if (isHardwareAccelerated() && getZ() != 0) {
damageShadowReceiver();
}
}
}
这⾥会通过调⽤mParent的invalidateChild()⽅法，来触发⽗类对于dirty区域的调整（可能会调整可能还是原区域）及改区域相对坐标的调整。进⼊ViewGroup.invalidateChild()⽅法。
@Override
public final void invalidateChild(View child, final Rect dirty) {
ViewParent parent = this;
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
// If the child is drawing an animation, we want to copy this flag onto
// ourselves and the parent to make sure the invalidate request goes
// through
//drawAnimation记录调⽤该⽅法的⼦View是否正在执⾏动画
final boolean drawAnimation = (child.mPrivateFlags & PFLAG_DRAW_ANIMATION)
== PFLAG_DRAW_ANIMATION;
// Check whether the child that requests the invalidate is fully opaque
// Views being animated or transformed are not considered opaque because we may
// be invalidating their old position and need the parent to paint behind them.
//调⽤该⽅法的⼦View是否不透明：处于不透明状态且没有在执⾏动画且变化矩阵没有变化
//Matrix可以⽤于View的平移、缩放、扩放、旋转等操作，⽐如某些应⽤上的双指缩放功能
Matrix childMatrix = Matrix();
final boolean isOpaque = child.isOpaque() && !drawAnimation &&
/
/ Mark the child as dirty, using the appropriate flag
// Make sure we do not set both flags at the same time
int opaqueFlag = isOpaque ? PFLAG_DIRTY_OPAQUE : PFLAG_DIRTY;
if (child.mLayerType != LAYER_TYPE_NONE) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
final int[] location = attachInfo.mInvalidateChildLocation;
//记录⼦View边界距离⽗View左边界和上边界的距离到Location中，⽤于下⼀段代码中的计算
location[CHILD_LEFT_INDEX] = child.mLeft;
location[CHILD_TOP_INDEX] = child.mTop;
//如果⼦View设置了变换矩阵，则根据变换矩阵调整dirty区域
if (!childMatrix.isIdentity() ||
(mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) {
RectF boundingRect = attachInfo.mTmpTransformRect;
boundingRect.set(dirty);
Matrix transformMatrix;
if ((mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) {
Transformation t = attachInfo.mTmpTransformation;
boolean transformed = getChildStaticTransformation(child, t);
if (transformed) {
transformMatrix = attachInfo.mTmpMatrix;
transformMatrix.Matrix());
if (!childMatrix.isIdentity()) {
transformMatrix.preConcat(childMatrix);
}
} else {
transformMatrix = childMatrix;
}
} else {
transformMatrix = childMatrix;
}
transformMatrix.mapRect(boundingRect);
dirty.set((int) Math.floor(boundingRect.left),
(int) Math.p),
(int) il(boundingRect.right),
(int) il(boundingRect.bottom));
}
//这是⼀个从当前的布局View向上不断遍历当前布局View的⽗布局，最后遍历到ViewRootImpl的循环do {
View view = null;
//parent可能为ViewGroup类型，也可能为ViewRootImpl类型
//最后⼀次循环执⾏时为ViewRootImpl类型
if (parent instanceof View) {
view = (View) parent;
}
//如果⼦View正在执⾏动画，设置遍历的⽗布局View的动画标识
if (drawAnimation) {
if (view != null) {
view.mPrivateFlags |= PFLAG_DRAW_ANIMATION;
} else if (parent instanceof ViewRootImpl) {
((ViewRootImpl) parent).mIsAnimating = true;
}
}
// If the parent is dirty opaque or not dirty, mark it dirty with the opaque
// flag coming from the child that initiated the invalidate
//设置当前ViewGroup的Dirty标识，表⽰当前的ViewGroup需要重绘
if (view != null) {
if ((view.mViewFlags & FADING_EDGE_MASK) != 0 &&
opaqueFlag = PFLAG_DIRTY;
}
if ((view.mPrivateFlags & PFLAG_DIRTY_MASK) != PFLAG_DIRTY) {
view.mPrivateFlags = (view.mPrivateFlags & ~PFLAG_DIRTY_MASK) | opaqueFlag;
}
}
//调⽤当前布局View的invalidateChildParent()⽅法，返回的值为当前布局View的⽗布局
//通过循环向上调⽤，最后返回的根布局是ViewRootImpl对象
parent = parent.invalidateChildInParent(location, dirty);
if (view != null) {
// Account for transform on current parent
Matrix m = Matrix();
if (!m.isIdentity()) {
RectF boundingRect = attachInfo.mTmpTransformRect;
boundingRect.set(dirty);
m.mapRect(boundingRect);
dirty.set((int) Math.floor(boundingRect.left),
(int) Math.p),
(int) il(boundingRect.right),
(int) il(boundingRect.bottom));
}
}
} while (parent != null);
}
}
在do-while循环中会调⽤到parent = parent.invalidateChildInParent(location, dirty)，这⾥执⾏到ViewGroup.invalidateChildInParent()⽅法。
@Override
public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {
//
if ((mPrivateFlags & PFLAG_DRAWN) == PFLAG_DRAWN ||
(mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID) {
//如果ViewGroup有没有动画执⾏或者动画已经完成
if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) !=
FLAG_OPTIMIZE_INVALIDATE) {
//dirty记录的是最开始调到invalidate()的View的区域
//dirty的四个坐标值值在执⾏下⾯代码是相对于当前循环到上⼀个ViewGroup来确定的
//这⾥做了⼀个偏移动作，偏移的量是当前上⼀个ViewGroup相对于现在ViewGroup的偏移值
//做完下⾯的偏移操作后，dirty的四个坐标就是想对于当前ViewGroup的坐标值了
dirty.offset([CHILD_LEFT_INDEX] - mScrollX,
location[CHILD_TOP_INDEX] - mScrollY);
//如果当前ViewGroup需要裁剪View
//则将当前ViewGroup的区域与View的区域做求并集的操作
if ((mGroupFlags & FLAG_CLIP_CHILDREN) == 0) {
dirty.union(0, 0, mRight - mLeft, mBottom - mTop);
}
final int left = mLeft;
final int top = mTop;
//如果当前ViewGroup需要裁剪View，且ViewGroup区域与View区域没有并集，则dirty置空
if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) {
if (!dirty.intersect(0, 0, mRight - left, mBottom - top)) {
dirty.setEmpty();
}
}
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
//⽤于循环到下⼀个ViewGroup时做offset操作
location[CHILD_LEFT_INDEX] = left;
location[CHILD_TOP_INDEX] = top;
if (mLayerType != LAYER_TYPE_NONE) {
mPrivateFlags |= PFLAG_INVALIDATED;
}
return mParent;
} else {//如果当前ViewGroup中有动画要执⾏
mPrivateFlags &= ~PFLAG_DRAWN & ~PFLAG_DRAWING_CACHE_VALID;
location[CHILD_LEFT_INDEX] = mLeft;
location[CHILD_TOP_INDEX] = mTop;
//如果需要对⼦View裁剪则设置dirty为当前ViewGroup区域
//如果不需要则求当前ViewGroup区域与原ditry区域并集
if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) {
dirty.set(0, 0, mRight - mLeft, mBottom - mTop);
} else {
// in case the dirty rect extends outside the bounds of this container
dirty.union(0, 0, mRight - mLeft, mBottom - mTop);
}
if (mLayerType != LAYER_TYPE_NONE) {
mPrivateFlags |= PFLAG_INVALIDATED;
}
return mParent;
}
}
return null;
}
invalidateChildInParent()主要是完成了dirty区域在调⽤该⽅法的ViewGroup中的更新，dirty指⽰的区域就是需要重绘制的区域。如果ViewGroup没有动画在执⾏，则dirty区域还是原来的区域，只需要通过偏移操作更改该区域的坐标值从相对于上⼀个ViewGroup（⽗ViewGroup），到相对于当前ViewGroup；如果有动画要执⾏，则表⽰当前整个ViewGroup都需要重绘，更改dirty值为当前ViewGroup 区域。
do-while最后⼀次循环最后会调⽤到ViewRootImpl.invalidateChildInParent()⽅法，进⼊该代码。
@Override
public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
checkThread();
if (DEBUG_DRAW) Log.v(mTag, "Invalidate child: " + dirty);
//如果传⼊⼀个null drity，则表⽰要重绘当前ViewRootImpl指⽰的整个区域
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